Broadband uhf dipole antenna



April 28, 1970 NORIYUKI KAWAMOTO ETAL 3,509,575

BROADBAND UHF DIPOLE ANTENNA Filed Ilay 9. 1968 3 Sheets-Sheet 1 M02: run K414414010, Ksmrz KATAYAMA,ANO

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ATTORNEYS United States Patent US. Cl. 343-795 6 Claims ABSTRACT OF THE DISCLOSURE A broad band antenna comprising two groups of antenna elements, each of which consists of at least one pair of antenna elements. One of the groups of antenna elements has a second-resonance at an approximate center frequency of a desired frequency band. The other group of antenna elements has a second-resonance at a frequency higher by 1.1 to 1.8 times that of said approximate center frequency. The two groups of antenna elements are closely positioned in parallel with each other so that the space between them is less than 0.2 of a wave-length at the center frequency. One of the groups of antenna elements has two terminals and supplies a signal to a receiver from the antenna at the inner ends thereof, and the other group of antenna elements is open circuited at the inner ends thereof.

FIELD OF THE INVENTION This invention relates to a receiving or a transmitting antenna for use in wideband communication for the VHF and UHF bands and more particularly to an antenna for use as a driven element for a UHF television receiving antenna. The term driven element" designates an element which supplies a signal to the receiver from the receiving antenna.

PRIOR ART Constant characteristics of impedance over the wide frequency band of a UHF television signal are desired for a driven element of a UHF television receiving antenna.

The conventional UHF television receiving antenna, such as the yagi antenna, corner-reflector antenna, etc., has as a driven element a dipole antenna with a 0.7 wave length or a triangular dipole antenna. The frequency dependence of the characteristics of impedance of those antennas is almost constant near the center frequency, but is not satisfactory at the ends of the wide frequency band of a UHF television signal.

SUMMARY OF THE INVENTION An object of this invention is to provide an antenna characterized by an approximately constant frequency dependence of impedance throughout the wide frequency band of the UHF television signal.

DESCRIPTION OF THE PREFERRED EMBODIMENT This object of the present invention is achieved by a broadband antenna comprising a first group of antenna elements having a second-resonance at approximately the center frequency of a desired frequency band and a second group of antenna elements having a secondresonance at a frequency higher by 1.1 to 1.8 times that of said approximate center frequency. Said first group and said second group of antenna elements are placed close to and parallel to each other so that the space be- 3,509,575 Patented Apr. 28, 1970 tween them is smaller than 0.2 to a wave length at said approximate center frequency. One of said groups of antenna elements has two terminals at the center thereof which supply a signal to a receiver from the antenna, and the other is open-circuited at the center thereof.

The second-resonance referred to herein can be explained as follows: in general an antenna or an antenna element resonates at many frequencies. The resonance at the lowest resonant frequency is termed the first-resonance and the resonance at the second lowest resonant frequency is termed the second-resonance.

Said first group and said second group of antenna elements include at least one pair of antenna elements respectively. Said pair of antenna elements are two arbitrarily shaped conductive bodies. Said two arbitrarily shaped conductive bodies are essentially similar in shape and size and are closely positioned at one part thereof so as to form a symmetrical arrangement and to achieve an antenna action." The meaning of the expression antenna action" is that said pair of antenna elements can receive electro-rnagnetic waves and a signal can then be taken out of the elements, or the element can transmit electromagnetic waves when a signal is fed to said pair of antenna elements at the center thereof.

BRIEF DESCRIPTION OF THE DRAWINGS This and other objects will be more fully understood when considered in connection with the following detailed description taken together with the accompanying drawings wherein:

FIG. 1 is a. front view showing a simple and fundamental construction of an antenna according to the present invention;

FIGS. 2a and 2b are diagrammatic views showing an unbalanced mode and a balanced mode of the antenna shown in FIG. 1, respectively;

FIG. 3 is a front view showing another simple and fundamental construction of an antenna according to the present invention;

FIG. 4 and FIG. 5 are perspective views showing other constructions of an antenna according to the prese'nt invention;

FIGS. 6a and 6b are perspective views showing the construction and dimensions of antennas used for taking measurements; and

FIG. 7 shows the VSWR of the antennas of FIGS. 6a and 6b.

Referring to FIG. 1, a broad band antenna 50 comprises a first group -1 of antenna elements which includes at least one pair of antenna elements 2 and 2', and a second group 3 of antenna elements which includes at least one other pair of antenna elements 4 and 4. Said pair of antenna elements 2 and 2' are positioned close to each other at one end thereof in a coaxial and symmetrical arrangement to achieve an antenna action and such that the space between said pair of antenna elements 2 and 2' is smaller than 0.2 of a wave length at approximately the center frequency of the desired frequency band. Said other pair of antenna elements 4 and 4 are also positioned close to each other at one end thereof in a coaxial and symmetrical arrangement to achieve an antenna action and such that the space between said other pair of antenna elements 4 and 4' is smaller than 0.2 of a wave length at said approximate center frequency. Said first group 1 of antenna elements has a second-resonance at said approximate center frequency. Said second group 3' of antenna elements has a second-resonance at a frequency 1.1 to 1.8 times higher than that of said approximate center frequency and is positioned close to and parallel with said first group 1 of antenna elements so that the space between said first group 1 of antenna elements and said second group 3 of antenna elements is smaller than 0.2 of a wave length at said approximate center frequency. Said first group 1 of antenna elements has two terminals and 5' which supply a signal from the inner ends of the antenna to a receiver, and said second group 3 of antenna elements is open-circuited at the inner ends 6 and 6 thereof. The overall length 21 of said first group 1 of antenna elements is from 0.65 to 0.95 of a wavelength at said approximate center frequency and said first group 1 of antenna elements has a second-resonance at said approximate center frequency.

On the other hand, the overall length 21 of said second group 3 of antenna elements is from 0.4 to 0.6 of a wavelength at said approximate center frequency and said second group 3 of antenna elements has a second-resonance at a frequency 1.1 to 1.8 times higher than said approximate center frequency.

Referring to FIG. 2a, an unbalanced mode 60 of the antenna shown in FIG. 1 is shown diagrammatically. The antenna element corresponding to the element 2 in FIG. 1 is divided into two parts 8 and 9 on a line a-a' (FIG. 1), which cuts said antenna element 2 even with the outer end 7 of said antenna element 4, and is open-circuited between the ends and 11, as shown in FIG. 2a. The antenna element corresponding to the element 2' in FIG. 1 is also divided into two parts 8' and 9' by a line b-b' (FIG. 1), which cuts said antenna element 2' even with the outer end 7 of said other antenna element 4', and is opencircuited between the ends 10' and 11, as shown in FIG. 2a. A short circuit connection is provided between the inner end 5 of said part 8 and the inner end 6 of the antenna element 4, and between said end 10 of said part 8 and the outer end 7 of the antenna element 4. Said end 10 of said part 8 and said end 11 of said part 9 are connected through a voltage source v. A short circuit connection is provided between the inner end 5' of the said part 8' and said inner end 6' of the antenna element 4', and between said end 10' of said part 8' and said outer end 7 of the antenna element 4'. Said end 10' of said part 8 and said part 11 of said part 9' are also connected through a voltage source V. Said unbalanced mode 60 has two terminals 5 and 5' at the inner ends of parts 8 and -8'.

Referring to FIG. 2b, a balanced mode 70 of the antenna shown in FIG. 1 is diagrammatically shown. The parts 9 and 9 of the antenna elements 2 and 2' in FIG. 2a are removed. Said outer end 7 of the antenna element 4 is connected through a voltage source V to said end 10 of said part 8; and said outer end 7' of the antenna element 4' is connected through another voltage source V to said end 10' of said part 8'.

A short circuit connection is provided between said inner end 5 of part 8 and said inner end 6' of the antenna element 4', and also between said inner end 5' of part 8 and said inner end 6 of the antenna element 4. Said balanced mode 70 has two terminals 5 and 5' at the inner ends of parts 8 and 8'.

The input impedance 2 at the terminals 5 and 5 of the antenna, in FIG. 1, is expressed by the equation:

where the V,, is a voltage division factor of said pair of antenna elements 2 and 2'. The impedance Z is the input impedance at the terminals 5 and 5' of the unbalanced mode of FIG. 2a. The impedance 2,, is the input impedance at the terminals 5 and 5' of the balanced mode of FIG. 26.

An electrical irregularity appears in the vicinity of said lines a-a' and b-b in FIG. 1. These irregularities require said voltage sources V and V, as shown in FIGS. 2a and 2b. The values of said voltages V and V are determined by the construction and dimensions of the antenna in FIG. 1.

The impedance Z is complicated due to the existence of said voltage source V. However, it can be assumed that said voltage source V is equal to zero, and that a short circuit connection is provided between said ends 10 and I1, and between said ends 10' and 11', in FIG. 2a, when the differences between the lengths of the antenna elements 2 and 4 and between the lengths of antenna elements 2 and 4 are not large. Therefore, the impedance Z, can be assumed to be the input impedance of a dipole antenna with a length of 21 It can further be assumed that said impedance 2,, is second-resonant at said approximate center frequency, and thus is composed of a real part which has an almost constant value over a wide frequency band and an imaginary part equal to zero, a positive value, or a negative value at said approximate center frequency, lower frequencies or higher frequencies, respectively.

The impedance 2,, is composed not only of an imaginary part, but also of a real part, which results from the existence of said voltage source V. It can be assumed that said voltage source V is equal to zero and that an open circuit is provided between said end 10 and the outer end 7 of the element 4, in FIG. 2b, and also between said end 10' and the outer end 7 of the element 4', in FIG. 2b, when the differences between the lengths of the antenna elements 2 and 4 and between the lengths of the antenna elements 2' and 4' are not large. There fore, the impedance 2,, can be assumed to be the input impedance of a parallel transmission line with a length of and to have only the imaginary part which has the characteristic of where h is the wave length.

Thus it can be seen that the imaginary portion of the impedance 2,, may be zero, a negative value, or a positive value at said approximate center frequency (2, 0.25 wave length), lower frequencies or higher frequencies, respectively.

From Equation 1, it is seen that the antenna shown in FIG. 1 is the equivalent to a series connection of said unbalanced mode in FIG. 2a and the balanced mode in FIG. 2b and the imaginary part of the impedance of each mode is cancelled out and the change of the real part of the impedance is small over a wide frequency band. Consequently, it is easily understood that the characteristics of the impedance of the antenna shown in FIG. 1 are almost constant over a wide frequency band.

Referring to FIG. 3, an antenna 50a is constructed similarly to that of the antenna shown in FIG. 1, except for the terminals 6 and 6'. The antenna 50a has the terminals 6 and 6' which supply a signal from the antenna to a receiver, at the inner ends of said second group 3a of antenna elements, which is shorter than said first group In of antenna elements. The input impedance Z at the terminals 6 and 6' of the antenna 50a is also represented by Equation 1, where V is a voltage division factor of said pair of antenna elements 4 and 4. The unbalanced mode and the balanced mode of the antenna of FIG. 3 can be shown by figures similar to FIGS. 2a and 21:, respectively, as could the unbalanced mode and balanced mode of the antenna of FIG. 1.

Since the value of the voltage division factor V can be changed from zero to one by adjusting the diameter of the-antenna elements 2 and 2' and the antenna elomcnts 4 and 4', the characteristics of the input impedance of the antenna, shown-constant over a wide frequency band in a manner similar to that of the antenna shown in FIG. 1.

The above description concerns the fundamental theory of this invention. Other constructions of this invention will be described below.

Referring to FIG. 4, another embodiment of an antenna 50b according to this invention is shown. A pair of triangular conductive sheets 12 and 12' form the aforesaid first group lb of antenna elements and a pair of conductive bars 13 and 13' form the aforesaid second group 3b of antenna elements. The antenna 50b has two terminals 14 and 14' which supply a signal from the ments is open-circuited at the center tthereof.

Referring to FIG. 5, still another embodiment 500 of an antenna according to this invention is shown. Two pairs of conductive bars 16, 16', and 17, 17 form the aforesaid first group of antenna elements and a pair of straight conductive bars 18 and 18' form the aforesaid second group 3c of antenna elements. The inner ends of the conductive bars 16 and 17, and inner ends of the conductive bars 16' and 17 are connected together, respectively, to form V-shaped elements. The antenna 500 has two terminals 19 and 19' which supply a signal from group 3c of antenna elements while the first group 1c of antenna elements is open-circuited at the center thereof.

Referring to FIG. 6b, an antenna 50b is constructed similarly to the antenna shown in FIG. 4 and has two terminals 22 and 22', which supply a signal from the antenna to a receiver, located at the inner ends of the second group 3b of antenna elements, while the first group 1b of antenna elements is open-circuited at the center thereof. The dimensions of each portion of the antenna 50b are given in FIG. 6b.

Referring to FIG. 7, the curves a and b represent the measured VSWR of the antenna at terminals 21 and 21' in FIG. 6a, and at the terminals 22 and 22 in FIG. 6b, respectively, the VSWR being one expression of the characteristics of impedance. The curves a and b quency band.

and the curve b shows that the VSWR is smaller than 2.0 in the range from 21:- Y l 1.45 to When the antennas of the present invention, as shown in FIGS. 1, 3, 4, 5, 6a and 6b, are used in practice, each pair of antenna elements are fixed to insulating materials by any available method at the vicinity of the inner ends thereof.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

l. A broad band antenna comprising a first group of antenna elements thereof.

greater than the length of said second group of antenna elements and said second group of antenna elements has the means for taking out a signal and said first group of antenna elements is open-circuited at the opposed ends thereof.

to form a symmetrical arrangement and to achieve an antenna action.

5. A broad band antenna as claimed in claim 1 wherein one pair of antenna elements consists of two triangular conductive sheets having essentially similar shapes and size and positioned close together at one vertex thereof so as to form a symmetrical arrangement and to achieve an antenna action.

essentially of the same size and shape as each other; the vertexes of said two conductive bodies being closely positioned so as to form a symmetrical arrangement and :6 achieve an antenna action.

References Cited UNITED STATES PATENTS 

